1. Field of the Invention
The present invention relates to a coin type vibrating motor, and more particularly to a coin type vibrating motor, which prevents oil, emitted from an oilless metal bearing provided on a shaft, from being scattered toward contact regions between a commutator and brushes, when the motor is driven, to prevent electrical short, reduces the number of required components to reduce production costs, and improves assembling efficiency.
2. Description of the Related Art
Generally, sound and vibration are mainly used by communication devices to inform users of an incoming call. In order to generate the vibration, a small-sized vibrating motor is driven so that the driving force of the vibrating motor is transmitted to a housing of a device, thereby vibrating the whole portions of the device.
Vibrating motors applied to the communication devices, such as a portable communication terminal, are divided into a flat type vibrating motor (also, referred to as a coin type vibrating motor) and a cylindrical type vibrating motor (also, referred to as a bar type vibrating motor).
The coin type vibrating motor generates vibration through a simple structure in which a weight having a high specific gravity is disposed and rotated, and is manufactured in a thin thickness, thereby facilitating the miniaturization of portable terminals. Thus, the coin type vibrating motor has been widely used.
FIG. 1 is an exploded perspective view of a conventional coin type vibrating motor, and FIG. 2 is a longitudinal-sectional view of the conventional coin type vibrating motor. As shown in FIGS. 1 and 2, the conventional coin type vibrating motor 1 comprises a rotor assembly 10 (hereinafter, referred to as a “rotor”) serving as a rotary member, a stator assembly 20 (hereinafter, referred to as a “stator”) serving as a stationary member, and a housing 30 for accommodating the rotor 10 and the stator 20.
That is, the rotor 10 is rotatably installed in the housing 30, and includes an upper base 11 provided with wound coils 12, a weight 13 eccentrically disposed adjacent to the wound coils 12, and an insulator 14 for protecting the upper base 11 and the weight 13 from the external environment. A commutator 15, including a plurality of segments divided and spaced from each other by designated intervals in a circumferential direction, is placed on the lower surface of the upper base 11, and a lower surface of the commutator 15 is exposed to the outside. The segments of the commutator 15 elastically contact upper ends of a pair of brushes 25, of which lower ends are fixed to the stator 20.
The stator 20 is placed on a bracket 35 closing the opened lower surface of housing 30, and includes a lower base 21 mounted on the bracket 35, a ring-shaped magnet 22 mounted on the upper surface of the lower base 21 and provided with N and S poles alternately arranged in a circumferential direction, and a power supply unit 23 electrically connected to a lead wire (not shown) for supplying external power and placed on one side of the upper surface of the lower base 21.
The lower ends of a pair of the brushes 25, of which upper ends are elastically supported by the commutator 15 of the rotor 10, are electrically connected to a positive terminal 23a and a negative terminal 23b of the power supply unit 23 so that different polar currents, i.e., anode (+) and cathode (−) are respectively supplied to the positive and negative terminals 23a and 23b. 
The rotor 10 is rotatably assembled with the central area of the upper surface of the bracket 35 by means of a bearing member 32 of a shaft 31 vertically placed on the central area of the upper surface of the bracket 35. Here, the bearing member 32 is embedded by the insulator 14 of the rotor 10, and upper and lower ends of the shaft 31 are respectively supported by upper and lower shaft supporters 31a and 31b provided on the upper surface of the bracket 35 and the lower surface of the housing 30. Further, upper and lower washers 34a and 34b are respectively placed on the upper and lower shaft supporters 31a and 31b. 
When external power is applied to the above-described coin type vibrating motor 1, different polar currents are induced to a pair of the brushes 25. Such currents supply power to the wound coils 12 of the rotor 10 along a circuit pattern of the upper base 11 through the commutator 15 contacting the upper ends of a pair of the brushes 25.
The rotor 10 is rotated in one direction centering on the shaft 31 by interaction between an electric field generated in the flow of the current induced in the wound coils 12 and a magnetic field generated by the magnet 22 of the stator 20.
Whenever the rotor 10 is rotated, contact points between the brushes 25 and the segments of the commutator 15 contacting the brushes 25 are changed so that the polarity of the power continuously varies. In this case, the rotor 10 having the eccentric center of gravity is continuously rotated, thereby inducing vibration serving as an incoming call signal.
An oilless metal bearing, which does not require a lubricating oil, is used as the bearing member 32 placed on the outer periphery of the shaft 31 for reducing the friction between the shaft 31 and the rotor 30. When such an oilless metal bearing is manufactured by sintering, the oilless metal bearing is impregnated with oil of a designated amount.
When the above-described vibrating motor 1 is rotated, the bearing member 32 of the rotor 10 rotated at a high speed in one direction emits and scatters the oil contained therein to the outside by centrifugal force. The scattered oil contaminates a pattern circuit printed on the lower surface of the upper base 11 and the upper surface of the lower base 21.
Fine metal powders are produced due to the mechanical friction between the commutator 15 and the brushes 25 made of a metal. In case that the oil emitted from the bearing member 32 is scattered to the contact points between the commutator 15 and the brushes 25, the scattered oil and the fine metal powders are burnt by electric sparks generated by friction and produce foreign substances such as black powders, and the foreign substances are not emitted to the outside but remain in the housing 30.
In case that nonconductive substances of the foreign substances are caught in the contact points between the commutator 15 and the brushes 25, the nonconductive substances generate a section, which is not electrically connected. On the other hand, in case that conductive substances of the foreign substances are caught in gaps between the segments of the commutator 15, there the conductive substances generate electrical short, thereby reducing the lifespan, performance and reliability of the vibrating motor 1.
The lower washer 34b is placed on the shaft 31 for preventing the contact between the upper base 11 of the rotor 10 and the magnet 22 of the stator 20. During the assembling process of the vibrating motor 1, the inaccurate assembly of the lower washer 34b, which is mounted on the lower shaft supporter 31b, with the lower part of the shaft 31 causes failures of finished products and reduces assembling efficiency of the vibrating motor 1.